This disclosure relates to methods for phenol production and, more particularly, to systems and methods for purifying cumene hydroperoxide cleavage products.
Processes for preparing phenol are well known. The cumene method comprises two stages: the first one is cumene oxidation by air oxygen to cumene hydroperoxide (CHP), and the second one is CHP acidic catalytic cleavage (decomposition) to phenol and acetone. After producing and cleaving cumene hydroperoxide (CHP), the resultant cumene hydroperoxide cleavage product mixture contains phenol and acetone as the principal products together with varying amounts of impurities, e.g., alpha-methylstyrene, acetophenone, mesityl oxide, cumene, acetaldehyde, hydroxyacetone, and residual acid catalyst, e.g., sulfuric acid catalyst. Before the products can be recovered it is necessary to remove or neutralize the acid catalyst in the CHP cleavage product mixtures since the presence of the acid catalyst in the subsequent distillation interferes with efficient recovery of the product and by-products of the reaction, in addition to causing corrosion of the distillation equipment.
Commercially, the residual sulfuric acid catalyst present in the cleavage product mixture is neutralized with an aqueous alkaline solution, e.g., aqueous sodium hydroxide. The resulting concentrated aqueous sodium sulfate salt solution formed from the sulfuric acid and the sodium hydroxide reaction is then separated from the main organic mixture using a series of liquid-liquid extraction operations. The resulting organic mixture, now free of sulfuric acid, is then subjected to a series of fractional distillations to recover the products and various components.
U.S. Pat. Nos. 2,734,085; 2,744,143; 3,931,339; and 5,510,543 variously teach conducting the cleavage acid extraction/neutralization step as a liquid-liquid extraction process in a reactor utilizing a circulating aqueous solution of concentrated sodium sulfate salt, i.e., the extractant, formed in situ by the reaction of sodium hydroxide and sulfuric acid. It is known that hydroxyacetone is typically present in an amount of 1,200-2,200 parts per million (ppm) concentration in the CHP cleavage product mixture prior to neutralization. During neutralization the hydroxyacetone equilibrates and partitions into two phases (organic and aqueous) within the neutralizer vessel in about equal concentrations. Hydroxyacetone is particularly troublesome to remove from phenol as it co-distills with phenol during the downstream rectification processes and contaminates the final phenol product. Although hydroxyacetone may be present in only minute quantities in the final phenol product, the hydroxyacetone impurity has color-forming tendencies and its presence renders the phenol product quality unacceptable for many end use applications, such as bisphenol A and polycarbonate.
To prevent this, U.S. Pat. Nos. 3,335,070; 3,454,653; 3,692,845; 5,502,259; and 6,066,767 variously teach removing hydroxyacetone from phenol via condensation reactions and conversion to higher boiling point materials, which create by-products that can be more easily separated from phenol in subsequent distillation steps. Both homogeneous and heterogeneous processes are described which use both basic and acidic treating agents on the organic streams to promote hydroxyacetone condensation reactions, such as sodium hydroxide, amines, ion exchange resins and zeolites. However, this treatment method is only partially effective because a new impurity 2-methybenzofuran (2MBF) forms, which is also very difficult to remove from phenol by distillation. This problem is particularly troublesome as its presence also renders the phenol product quality unacceptable for many end use applications.
In the conversion of hydroxyacetone to higher boiling point materials, U.S. Pat. No. 6,066,767 (""767 patent) describes a process for purifying phenol using sodium hydroxide and alkaline agents as treatment agents to promote deep condensation reactions of hydroxyacetone to high boiling point materials purportedly free of 2MBF. In this process the CHP cleavage product mixture is extracted with 10-20 weight percent (wt. %) sodium sulfate salt solution according to conventional methods, and the hydroxyacetone contained within the aqueous salt phase is treated with sodium hydroxide reagent to form deep condensation products which recycle into the process and mix with the phenol-acetone stream for later removal.
Several drawbacks are associated with the method of the ""767 patent. First, there are high raw material costs associated with the neutralizing reagents. In the ""767 method, to effectively neutralize the acidic 10-20 wt. % sodium sulfate aqueous stream large quantities of sodium hydroxide must be added to neutralize and maintain the excess alkalinity required to provide catalysis. In response to this quantity of sodium hydroxide additional sulfuric acid must be purchased and utilized to neutralize the sodium hydroxide so as to maintain the critical pH control range while neutralizing the CHP cleavage product mixture. Thus raw material costs are significant for the ""767 process.
Secondly, alkaline phenol salts (e.g., sodium phenolate) form, which can cause pH fluctuations, incomplete phase separations during neutralization, and contribute to downstream fouling of equipment. If the alkaline phenol salts cause pH fluctuations, and the critical pH control range cannot be maintained, emulsions may form and render various equipment useless. Third, the ""767 patent acknowledges that unidentified deep condensation products formed from hydroxyacetone re-enter the organic stream and recycle into the process. These unknown condensation products can potentially contaminate the final phenol product and risk causing other quality and equipment problems. Fourth, the process disclosed in the ""767 patent employs multiple extraction stages to optimize the removal of hydroxyacetone. These multiple extraction stages require additional time, labor, materials and equipment to implement, thus increasing costs to remove hydroxyacetone to acceptable levels in the final phenol product.
Accordingly there remains a need in the art for a method and system for removing hydroxyacetone and other impurities from cumene hydroperoxide cleavage products to acceptable levels.
A method for removing impurities from a cumene hydroperoxide cleavage product mixture comprises heating an aqueous salt phase containing impurities at a temperature and for a time sufficient in a non-alkaline environment to form water-soluble derivatives of the impurities; combining the aqueous salt phase containing the water-soluble derivatives with a cumene hydroperoxide cleavage product mixture to form a combined product mixture; and separating the aqueous salt phase containing the water-soluble derivatives of the impurities from the combined product mixture.
In another embodiment, the method for removing impurities from a cumene hydroperoxide cleavage product mixture comprises heating an aqueous salt phase containing impurities at a temperature and for a time sufficient to form water-soluble derivatives of the impurities, wherein heating comprises heating the aqueous salt phase containing the impurities at a temperature of about 150 to about 350xc2x0 Celsius for about 0.5 to about 1.5 hours under a pressure of about 50 to about 1 500 pounds per square inch to the reaction mixture; combining the aqueous salt phase containing the water-soluble derivatives with a cumene hydroperoxide cleavage product mixture to form a combined product mixture; and separating the aqueous salt phase containing the water-soluble derivatives of the impurities from the combined product mixture.
A system for purifying a cumene hydroperoxide cleavage product mixture comprises means for heating an aqueous salt phase containing impurities at a temperature and for a time sufficient to form water-soluble derivatives of the impurities; means for combining the aqueous salt phase containing the water-soluble derivatives with a cumene hydroperoxide cleavage product mixture to form a combined product mixture; and means for separating the aqueous salt phase containing the water-soluble derivatives of the impurities from the combined product mixture.
In another embodiment, the system for purifying a cumene hydroperoxide cleavage product mixture comprises a cumene hydroperoxide cleavage product mixture feed containing impurities in fluid communication with an aqueous alkaline solution feed; the cumene hydroperoxide cleavage product mixture and aqueous alkaline solution feeds are in fluid communication with a neutralization drum having an aqueous salt phase outlet; an aqueous salt phase feed containing impurities in fluid communication with a heat treatment vessel having a heat-treated aqueous salt phase outlet; and a heat-treated aqueous salt phase feed containing water-soluble derivatives of the impurities in fluid communication with the cumene hydroperoxide cleavage product mixture prior to the neutralization drum.